help with preamplifier

skobo · 14th July 2005, 01:33 PM

I have an old guitar amp with four 2N3055 transistors, but i dont have a preamplifier for it. So i wanted to built a preamplifier for it. I attached a schematic of the preamp i want to build. Is this a good idea? If anyone have any suggestions please tell me

Fritzell · 14th July 2005, 04:07 PM

Looks like a standard op amp circuit. It will sure work, but i'm little unsure about the passive filter. Then if not the input impedance on you power amp is very low i think you can skip the emitter following transistor. If you want to make it really easy you can skip the whole second op. I built a preamp for a bass amp with just one input/preamping op then an active filter . Works fine

richie00boy · 14th July 2005, 04:25 PM

No, you can only skip the emitter follower output if the input impdance of the power amp is very high.

sam9 · 14th July 2005, 05:06 PM

Yes it's a good circuit.

However, it also carries the ESP logo. Rod Elliott holds the copyright. You should get his permission by before posting the image here.

Virtually everyone on this forum is familiar with ESP so you could simply refer to the project number and thus avoid any concerns about posting copyrighted materials.

edl · 14th July 2005, 07:11 PM

project27
project27b

asc · 15th July 2005, 12:43 AM

I'm considering building a double opamp based preamp for a bass guitar. I've seen many different suggestions for the actual opamp chip. What can I use to differentiate them?

-ASC

skobo · 15th July 2005, 01:50 AM

edl thanks for the links

the preamp that i wanted to use is actully the preamp from project 27. It says that input sensitivity of amplifier must be about 750mV for full output! How can I know what is the input sensitivity of the amp I have?

skobo · 15th July 2005, 12:02 PM

One more thing the power suply of the amp is 2x80V how can i reduce this voltage to 15 V that i need for preamp? Can I use the original schematic that is given with preamp, and what changes should i make?

Fritzell · 15th July 2005, 12:11 PM

The opamp takes very little current so you can use a zenerdiod to stabilize the voltage. Put a 15V 1W zener in series with 3.3K 2W (or more) resistor

edit: Yes you can use the circuit; Just change the resistor to 3.3K at least 2W.

jaycee · 15th July 2005, 12:54 PM

Rod Elliot has a "pre-regulator" project on his site designed just for this purpose.

14th July 2005, 01:33 PM	#1
skobo diyAudio Member Join Date: Jun 2005 Location: Uzice	help with preamplifier I have an old guitar amp with four 2N3055 transistors, but i dont have a preamplifier for it. So i wanted to built a preamplifier for it. I attached a schematic of the preamp i want to build. Is this a good idea? If anyone have any suggestions please tell me

14th July 2005, 04:25 PM	#3
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	No, you can only skip the emitter follower output if the input impdance of the power amp is very high. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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14th July 2005, 04:07 PM	#2
Fritzell diyAudio Member Join Date: Jul 2004 Location: Sweden	Looks like a standard op amp circuit. It will sure work, but i'm little unsure about the passive filter. Then if not the input impedance on you power amp is very low i think you can skip the emitter following transistor. If you want to make it really easy you can skip the whole second op. I built a preamp for a bass amp with just one input/preamping op then an active filter . Works fine

14th July 2005, 05:06 PM	#4
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	Yes it's a good circuit. However, it also carries the ESP logo. Rod Elliott holds the copyright. You should get his permission by before posting the image here. Virtually everyone on this forum is familiar with ESP so you could simply refer to the project number and thus avoid any concerns about posting copyrighted materials.

14th July 2005, 07:11 PM	#5
edl diyAudio Member Join Date: Oct 2004	project27 project27b

15th July 2005, 12:43 AM	#6
asc diyAudio Member Join Date: Jul 2005 Location: Portland, OR	I'm considering building a double opamp based preamp for a bass guitar. I've seen many different suggestions for the actual opamp chip. What can I use to differentiate them? -ASC

15th July 2005, 01:50 AM	#7
skobo diyAudio Member Join Date: Jun 2005 Location: Uzice	edl thanks for the links the preamp that i wanted to use is actully the preamp from project 27. It says that input sensitivity of amplifier must be about 750mV for full output! How can I know what is the input sensitivity of the amp I have?

15th July 2005, 12:02 PM	#8
skobo diyAudio Member Join Date: Jun 2005 Location: Uzice	One more thing the power suply of the amp is 2x80V how can i reduce this voltage to 15 V that i need for preamp? Can I use the original schematic that is given with preamp, and what changes should i make?

15th July 2005, 12:11 PM	#9
Fritzell diyAudio Member Join Date: Jul 2004 Location: Sweden	The opamp takes very little current so you can use a zenerdiod to stabilize the voltage. Put a 15V 1W zener in series with 3.3K 2W (or more) resistor edit: Yes you can use the circuit; Just change the resistor to 3.3K at least 2W.

15th July 2005, 12:54 PM	#10
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Rod Elliot has a "pre-regulator" project on his site designed just for this purpose.

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